The present invention relates to electrical load control systems in which the rate of power delivered to a plurality of loads is continuously measured and compared with a predetermined desired rate of consumption. If the monitored rate exceeds the desired rate, then one or more of the loads are disconnected (shed) and if the converse exists, then one or more of the loads are connected (added) to bring the rate of consumption of power up to the desired level.
Systems incorporating the principles of the present invention, as more fully described herein, can be adapted for a wide variety of applications. However, the invention is primarily intended for use in power monitoring and regulating systems designed for regulating electrical power consumption by utility customers. The efficiency for a utility depends to a large extent on the uniformity and predictability of the level of power required to meet the demands of the numerous utility users. In order to improve such efficiency, the utilities have adopted certain billing practices designed to encourage customers to even out their power consumption and to avoid temporary overloads that are incapable of being efficiently met by the power resources available at the utility's central station. One practice is to charge the customer according to a usage formula that includes a factor based on the actual energy consumed over a period of time, such as a month, and a factor based upon the maximum power consumption in one of a succession of short time intervals, referred to as the demand intervals. Typically each demand interval in 15, 30 or 60 minutes.
Utility meters such as the integrated-demand meter, have been developed for installation at the power entry point of the customers facility for measuring total energy consumed during a predetermined billing period, e.g. one month, and the maximum energy used during any one of the demand intervals. The billing rates based on the above-mentioned formula are applied so that the customer pays a disproportionately higher amount when he allows an overload condition to occur in any one of the demand intervals during the billing period. In other words, the customer pays less if he is able to regulate his loads so that he limits the maximum energy consumed during the brief demand interval, and instead, spreads the equivalent amount of energy out over a plurality of demand intervals. Existing power monitoring and regulating systems are installed to provide load regulation so as to avoid a large, temporary overload that might otherwise occur during any one of the relatively short demand intervals.
For large industrial customers, the utilities generally install a utility meter of the type that produces metering pulses representing the time lapse of each demand interval and representing the rate of power usage occurring within such interval. The utility itself has equipment for automatically counting metering pulses and uses the totals therefrom to calculate the customer's bill. For such installations, power monitoring and regulating systems are available to receive and process the metering pulses and to develop appropriate electrical control functions therefrom for regulating the number of loads connected to the power source. The regulation takes the form of adding loads when the rate of power is too low and shedding loads when the power consumption becomes excessive.
However, many utility customers, especially smaller, non-industrial businesses, are not equipped with a pulse-output type of demand meter. Instead, a type of less costly, demand meter is typically installed in which an electro-mechanical ratchet mechanism operates to register the maximum energy used during any one of the demand intervals occurring between monthly meter readings. Existing power monitoring and limiting systems of the type that receive electrical metering pulses, are not suited for customers having this type of meter installation.
Accordingly, one of the objects of the present invention is to provide an improved circuit and method for monitoring and regulating power consumption for use in installations where a pulse-type demand meter is not available.
More particularly it is an object of the present invention to monitor the rate of power consumption by means of an analog-type circuit and to convert the analog measurement into a digital-type output suitable for controlling the adding and shedding of electrical loads.
Another object of the present invention is to provide a circuit of the above-described type having the capability of regulating the loads so that an overload condition, if it does occur, can be corrected quickly enough so that it does not register on the demand meter as an excessive energy demand during the applicable demand interval.